what i did when i played 20-25 tables of low limits is to stagger start times and played in sets.
So i'd load 15 straight up, once they are loaded wait 5 minutes and load another 5, then wait another 5 minutes and load another 5 for my set of games. Just gave me some breathing room in late game if i ran well i tended to make more mistakes 2-3 handed as i had far less time.
If you want to make better use of your time, learning to play continuous is better. so perhaps stick with playing 15 but just continuously load them for longer periods and it should equal more volume over time and a more efficient way of doing things.
Also, try to just move up slowly, don't just go from 15 - 25/30 tables, it never works. Nothing good happens overnight, just let it come naturally as you add one table at a time while still being able to put the same amount of thought into decisions.
The other thing that can help is the use of programs like table ninja. I like to have one big main stack, then have hotkeys setup for tables that i want to concentrate more on, or 3 handed or HU play in general i can hit a hotkey and the table will pop up next to my main stack.
But just experiment to find out what works for you, i've tried pretty much every setup imaginable and settled for a multistack setup where i have 3 tables on my screen with 1-3 tables in each stack, then i have the 4th stack free for games i want to concentrate on. have all my hotkeys setup the way that i like, HUD is streamlined and easy to read in game all those things help a lot.
hope this babble helps.
PS. that's why you don't ever purchase a mac....