The player’s towns on the other forums are probably on VIP 15 and at least Player Level 60.
The lot cap 11 is maxed out for your Player Level 50. Reaching level 58 will unlock one and level 60 another. Then you can have 13 Sims on a lot. This is the max for all towns.
How many Sims can live in a house depends on your VIP and on your Player level. Your VIP is maxed out, but there are some more Player Levels to achieve. Level 57 and 59 each will unlock one more household Sim. I don’t know how many are allowed at VIP 15. With VIP 11 and Player Level 65 it’s 7.
The Sim cap for your town will also increase as you level up.
Hope, this helps :)