What is the upgrade path from 9.1.5 to 9.7 or 10.0?
Can we upgrade directly or is should we upgrade to an interim version first?
Another question: Can we leave the agents at 9.x version and upgrade only the MOM and EMs? Is this supported?
You can upgrade from 9.1.5 to 9.7 or 10.0 directly. Please check the sheet of Introscope Upgrades in compatibility guide.
http://www.ca.com/us/support/ca-support-online/product-content/status/compatibility-matrix/application-performance-management-compatibility-guide.aspx
Also, Agent version should be lower or same as EM version. (Agent version <= EM version)