I don't know which slide-out mechanism Forest River is using on the 2015 Solera "S" model - on our 2012 "S" we have the Lippert Flush Floor slide. If you search the Solera subforum, you will find lots of slide-out posts (Solera - Forest River Forums
Also, Lippert has manuals on the internet - this one looks very similar the the one in our 2012 "S" and includes a trouble shooting guide: http://dutchmen.com/image/data/docum...ice_Manual.pdf
Our slide-out is locked out - won't work - if the vehicle ignition is on - so be sure the vehicle is off.
Again on our 2012, I believe the slide-out is separately fused to the house batteries before the house disconnect switch. The slide-out works on ours with the house disconnect switch in the "off" position. I haven't had to find the fuse or circuit breaker, but I would start searching in that area - in the stair well, at the batteries, and around the disconnect switch. The back of the disconnect switch is accessible by removing the drawer below the kitchen sink (again, on our 2012).
Another thought - check for voltage at the slide-out switch - haven't done this, but I would try pulling the switch out of the panel and measuring for 12 volts (to ground, I believe) at the switch wires.
If you have the same slide-out as we have, you could check for voltage at the slide-out motor when the button is pressed. The motor is visible on ours through the propane door - mounted above the propane regulator. I believe there is a connector to the motor down there - accessible (with some difficulty) from below / through the propane compartment / or through the compartment behind the propane compartment). If you can disconnect that connector and test for 12 volts with your multimeter while someone activates the slideout switch - you can verify that power is getting to the motor. Hopefully, you will measure "0 volts" between the connector terminals and ground - proving an electrical (rather than motor) problem. For safety reasons, make sure the motor is disconnected when performing this test - you don't want the slide to start moving while you are reaching up there!
Of course, if you have a different slide-out mechanism (e.g., the Schwintech mechanism) all of the above is unrelated - google Lippert Schwintech to find a manual and/or troubleshooting guide.
Good Luck - I know slide-out issues just after purchase are quite infuriating - ours broke the motor mount off the frame on about the fifth slide-out actuation after purchase - also several hundred miles from the dealer.