15 foot RCA cables out of TT with no pre amp?

Im very limited with the space I have. This is kinda limiting me to keep the turntable on a 15’ cable. I’m using a Pro-ject Carbon Debut Evo with an Ortofon  2m blue to an Onkyo stereo with a phono input. Cables are midrange, nothing special but not total crap. Just wanted to get some opinions or suggestions on this. How bad the loss is gonna be if there is any. 
You want your TT and “stereo” as close together as possible, and see how it sounds. Or, get yourself a secondary phono stage and put that as close to your TT as possible and run the RCA’s out form it to the Onkyo.
As a temporary set up, if possible.
Place the Onkyo as close to the TT as possible and use a shorter IC.
Does Temporary arrangement require a Longer Speaker Cable ?

If it works you can then Try the Long and Short IC configuration.

Using a separate Phonostage, as already suggested, with the Onkyo will also offer other configuration options.  
You will be screwing up the high frequency response of the cartridge using a long cable. There are many inexpensive phono stages you can buy. Put it by the table and run the long cable from it.