I just started having the same issue with my wife's 2015 CX5 GT. She's racked up just over 64,000 miles since we bought it new in July 2014, so she used to drive ~100 miles/day until just recently when she got a promotion and now works from home and takes just short trips. I'm an automotive engineer and car tuner by trade with over 30 years experience and meticulously maintain my fleet of vehicles way above and beyond the FSM and use the highest quality fluids, parts, etc.
I tried to use my suction pump to extract some of the oil, but unfortunately even the smallest hose (which is the same OD/width as the dip stick) I couldn't get in far enough, so I had to change the oil & filter, even though I had another 3,000 miles to go. Since I didn't have a filter, I went to my local dealer and I have a great relationship with parts and service there and mentioned the fuel dilution problem I am now seeing and mentioned your post. Well, I got the typical "Never seen that before" answer, so I left and did an oil/filter change and only filled it halfway, just before the polar air arrived and temps got down to -15F for a few nights. I just checked the level tonight and it's already up to the full mark after only ~60 miles!
Compression tested good, no head gasket leak, no oil burning (Need some, lol!), the oil looks brand new, just smells like fuel. I'm going in tomorrow and having a serious discussion about this, as this is completely unacceptable.
I feel your pain and will keep you updated. Just glad I found someone with the same problem on the 2.5L petrol engine. Know all about the crap Mazda is playing with the diesel!