Inheriting a SOAP API project - how to improve performance

hi Devs

I was recently onboarded to maintain a SOAP-based API that integrates with multiple enterprise sources (Jupiter, MDM, etc.). My background is primarily REST APIs, so I'm trying to understand the architecture better.

My questions: 1. Why SOAP over REST/gRPC? - I understand SOAP is older, but why would enterprise systems stick with it when REST is simpler and gRPC is faster?

2. **Performance improvements** - My team wants to improve this API's performance. what are the most effective approaches?