http://ninjalitics.com works pretty good.
Both ninjalitics and socialblade drop only if you don't check your accounts' pages for a while, but if you check all of them on a regular basis you shouldn't experience any drop
If you prefer a custom and private solution you'd probably end spending something like 100 dollars
If I were you I'd rather code a script to check all my pages on ninjalitics,so they don't drop
But still I can't see the point in tracking all of your 1500 accounts; let's say you track all of them on a daily basis (which is a relatively easy task),you still have 1500 accounts and that's lots of datas to be handled.
This is really time consuming and I think you'd earn more by creating new accounts instead of tracking the already existing ones,but that's only my take and I don't know your business
