The reserved slots are not the cause of the server being full, if there are 20/18 players, there's only actually 18 playing, not 20. In other words, the server would still be full, and you would wait the same amount of time.
But when non-VIPs/non-regulars leave the server, do those VIPs/Admins "stay in" the vip/admin only slots, or do they get shunted into non-VIP/non-admin player slots? IF they DO [and only if, hence why I ask] get shunted to those non-VIP-only/non-admin-only slots then we have a problem since then, instead of taking only the slots that only they have access to, then they'd be taking up slots non-VIPs/non-Admins could be using to play.
But that all hinges, as I was / still am careful to note, on what happens if those slots are full and non-VIPs/non-Admins leave