Good question to ask and thank you both for responding.
I do wonder why would one still wish to use Elements 10, if one has installed Elements 15 and I would definitely want my Topaz plug-ins in 15.
l have also just upgraded to Sierra on my mac after several hours of problems, which Apple helped me to sort out. I really don't want to end up in a time-consuming and frustrating mess with my mac system, Photoshop and Topaz compatibility (or incompatibility). I have read of people having problems in Sierra with their Topaz products - something to do with the graphics card, which I hope Apple have now sorted a few months on.
I would be grateful for any more information on this.
Many Thanks
So far i haven't had any problems running topaz plugins on a MacBook Pro with macOS Sierra and several pse versions including 15.
There is a new 10.12.3 update fixes some graphical issues depending on what model mac you have.
https://support.apple.com/en-us/HT207462