I've seen a lot of people who seem to think that agents don't understand contracts, and I just don't think that's correct. Publishing contracts are very specialized, and agents are experts in navigating them. Perhaps you've had bad experiences? I don't know. But please don't just dismiss all agents and make it seem like they don't understand publishing contracts. That's a huge part of their job, and a good agent can and will get you better terms on the contract.
A literary or IP lawyer can look over foreign rights contracts, but an agent has a far better means to set up the initial conversation to make that contract *happen*, to know the reputations of the publishers and to know which rights mean more based on which countries. My agent knew, for example, which rights made more sense for me to keep in my Brazilian publishing contract vs. my German publishing contract; she knew which foreign publishers had better reputations and distribution and marketing, and she had the contacts to make those contracts happen in the first place.
I'm hybrid, and I can't imagine not working with my agent. She's already gotten me foreign contracts that are worth more than half a years sales on Amazon for this self published work. Heck yes, she's worth the 15% on that. She got that contract for me, hunted it out and made it happen, and I did no work for it. I'm in her foreign catalogue, and she goes to world rights fairs regularly, pushing my work.
She doesn't take a commission for the work I publish here because I do all the work. And I have no problem whatsoever with paying her for the work she does--because when she profits, I profit that much more.
For my traditionally published work, she's absolutely worth it there, too. She argued for a higher advance that more than paid her commission, plus 20+ foreign language rights.