I think @BrandonBerner can help even better as he's running more than 500 accounts im sure he has some experience as to how much a 150 will work.
Yeah, as usual, unless a host says they have dedicated core, you usually cannot run it at 100%. If there's a burst everyday at certain hour that will max out the CPU, i suppose it will be fine. But once you get the vps, you can continually monitor the CPU usage and see what it's like. It rarely hit 100% (maybe i haven't turn up the settings) for 24/7.
It's a pain, but then again some host allow at least a 7 day trial if you ask nicely. If you notice at around 3 days in and you are constantly at 100%, then send them a refund request and state your reason being (my app is eating too much of resource). If you go completely honest with them they /should/ be able to refund you. But of course these should be asked on pre-sales first and see if they can do that. Some don't like it that you went in and "abuse" their servers and ask for refund.
I saw a few post on LET saying contabo is dedicated resources. So you can use that. I don't know if you can, but mayb you can even try installing your own ISO. https://www.lowendtalk.com/discussion/comment/1080753/#Comment_1080753
One day, when i have some extra cash lying around i might try it.