I went back to work full time when my ds was 9 months old and to try and cut back on childcare expenses and spend more time with him I decided to work from home one day a week. I found it pretty easy at first, but as he grew older I felt I wasn't doing my job well that day or doing being a Mum very well either!
Up until he was one he would happily sit at my feet and play for ages, just happy I was there tapping away on my laptop whilst counting his own toes, but once he hit one I found that he was trying to get my attention so much I would just give up and not do anything until he went down for a nap, then just end up cramming it all in when I could and getting stressed out. He's so sussed now I've only got to turn the computer on when he's in the room to check my emails and he comes over, climbs on my lap and switches it off or pulls the wire out!
I ended up throwing in the towel and reducing my hours and much prefer a whole day with him unhampered by work worries (I just seem to spend the day shopping and cleaning now )...
I think that, depending on your lo, you'll probably be okay til he starts getting mobile and more demanding of Mummy's undivided attention, then if you have the option of spreading it out, sit down and work in the evenings and nap times. Don't expect to get a massive amount done whilst he's awake...
Not too negative I hope... if you've only got 15 hours a week to get done I reckon you'll be fine as long as you don't mind doing it in short chunks rather than solid sessions.