I have not ever had an issue with Sims not showing up to LN lot types unless for the intentional feature of it not being the current hot spot. Besides knowing where the current hotspot is, which changes, each LN lot type has its own peak time as well. Not to mention if you have a lot of Sims in the neighborhood with certain traits, they will not visit these types of lots. To find out where the hotspot is then either read the newspaper or go to the world map view to find it. Also it is possible that the reason why some may have issues with Sims not showing up to lots could be an inadequate CPU, as TS3 is a mostly CPU driven game. 2.4 GHz unless stated otherwise is the minimum for real-time simulation to function as intended. Otherwise, it will be reflected in gameplay and the most common side effect of this is when Sims are much less active because the computer hardware cannot handle anything more than that. Sim activity and the speed at which the system calculates for the A.I. is heavily affected by the CPU. Additionally, using any mods heavy on the CPU will likely affect the performance of TS3 as there is possibly too much fighting over the CPU's attention. This may not be a problem for those who have a higher than 2.4 GHz, and I would guess at least starting at 3.0 Ghz. According to my own experiences over the years with different computers, TS3 always performed the best for me with CPU's with higher GHz. Remember that TS3 never did release recommended system requirements, but I wonder what it would be if they had.
Now the mod you mentioned, I wouldn't recommend in terms of 15+ Sims and having that many unless one has a decent CPU to handle all those extra Sims getting simulated on screen all at once with a route fail free lot to handle all that Sim traffic as well. This is why these lot types have a maximum # of guests so to not overwhelm some computers that would not be able to keep up because remember TS3 was made in mind for the majority to play and why it was not catered for gaming computers. Fortunately because most can play but also unfortunately because TS3 has so much more potential that gets held back because it was not designed to take advantage of the most latest technology of its time.
According to the officially licensed game guide for The Sims 3 Late Night:
Peak Time: Between these hours, you are likely to see the maximum number of Sims in the bar.
Peak Day: Every bar type has a peak day when they pack 'em in. On other days, you risk showing up to a ghost town. Hot spots are designated on Map View with a red triangle.
Maximum # of Guests: This is the limit of Sims that can be inside the bar.
Unappreciated Traits: Sims with these traits are not likely to fit in very well at this type of bar.
Dive Bar
Peak Time: 2pm lunch crowd
Peak Days: Wednesday, Thursday
Maximum # of Guests: 8
Unappreciated Traits: Snob, Coward, Neat, Family-Orientated
Dance Club
Peak Time: Midnight
Peak Day: Saturday
Maximum # of Guests: 14
Unappreciated Traits: Frugal, Loner, Loser
Lounge
Peak Time: 11pm
Peak days: Friday, Saturday
Maximum # of Guests: 10
Unappreciated Traits: Frugal, Loner, Loser
The lot type, hang out, was updated to incorporate LN type hot spots which is great that they did that for those who want to bypass the maximum # of guests (or does it have a limit too?) or just have something of their own creative freedom without the LN lot type requirements. Though this lot type can be anything the player makes it, it does display a table with umbrella and chairs which resembles an open version of a restaurant. The diner I created inspired by Tom's Diner from Cyberpunk 2077, I classified as a hangout and it can get pretty busy sometimes. With Ani's version of the It's Business Time Industrial Oven, Sims do order to eat when they get hungry but also I have other activities so Sims can stick around longer, although my Sims are good at entertaining themselves too. I could not find anything in my prima guide about the description of the lot type of hang out but here:
https://sims.fandom.com/wiki/Hangout Indeed, Sims who visit hangouts are usually socializing a lot as well.
Tom's Diner (Hangout) The identical twin of the Sim below at the bar, but at this point her sister moved to Bridgeport and she lived alone with her three cats.
Chidori Club (Dance Club) Originally a different lot type, arcade, but I changed it in my game. My Sim is at the bar but sometimes if there is another household member I will switch to get the plumbob out of the screenshot instead of completely disabling the effects.
Something else to take into consideration, is all of the Sims jobs in the neighborhood which may have them working through peak days and/or peak times.
Previous Game: Batman: Arkham Knight (Hard Mode/Unfinished-Another Time)
Current Game(s): ObsCure and Cyberpunk 2077