No, I don't think the rise will affect drain speed. Flushing and siphoning is typical of not getting enough air in the drain system. A durso isn't going to cut it when you're dropping into a basement. A couple things you can try.
Tee off of the 15 vertical, towards the top, and glue in a vertical vent pipe made of pvc. Cap it and drill holes in the cap to allow air to enter.
Tee off of the top of the 3 foot rise and glue in a 2-3 foot tall vent pipe to allow air into the system. This one is a little trickier as you have to make sure your vent pipe is higher than what the water is backing up in the 15' section. Just a little trial and error.
You might also want to try to put a slope on the 10 foot horizontal section if possible.
Your setup is similar to mine. I have a 3 foot rise off the floor, over and into the sump and it works fine, although my drain line is 1.5". I have 3 different locations where I allow air to enter the system.
Hope this helps and makes sense.
