The Grandmother was my first synth . Great sounds. Terrible power supply ! The pitch wheel is a bit ‘ fragile’. The nuts around the inputs on the rear are plastic , not metal.
It took me a while to get to grips with patch cables, and making ‘proper’ and musical sounds 😬. It’s great for early Tangerine Dream , Klaus schulze stuff which I love .
Lots of droney watery sounds if you like that kind of thing .
About 6/7 months after buying it , Moog Sirin came out , which is desktop and has presets . No modular .sounds very similar otherwise.. Plus you have to have a midi keyboard to use it . It’s discontinued now and expensive .initially I was a little disgruntled as a compact Moog is better for space in my small musicroom .However although the Grandmother has no presets , you can do more with it imho.
There are quite a few official tips for the Grandmother from moog on you tube , and lots of unofficial ones. It may be worth checking those out, as id imagine you more or less have the same controls on your model 15.
The only other thing i’d say is if you can afford to do so , try and get either a DFAM or Behringher edge to go with it .
Hope this helps