Hi Wal,
By happy coincidence I too own a RST and do a 15 Mile round commute (or did up until last week, when I changed jobs, but that a different story). You will be racking up about 4000 miles a year so there are some things that WILL need to be looked at every so often. The problem is any maintained schedule is dependant on the quality of the components that you specified on your RST and also the conditions that you ride through. So below I have listed MY maintenance not yours!
First the MOST important thing to keep any bike in good condition is to clean it!!! When you are cleaning a bike you find all those little 'issues' that need to be sorted.
Brake blocks - I get about a year of use from my Cool stop salmon pads - others get very different mileage
Rims - VERY IMPORTANT - If you haven't got ceramic rims then you need to be checking these carefully after the 2nd year.
Chain, Chainring, Spur Gear - there are LOTS of posts on the life expectancy of chains. I have about 8000miles on mine. I expect it to get to 10,000 at which time I will reverse round the chainring and spur gear. I tighten the chain ~ every 6 months.
Gear & Brake Cables - When I first built up my RST I skimped on the cables even so they were still going strong 14 months later. I switched them out for better cables because I was looking for something to do! I would expect the high quality replacement cables to last at least 3 years.
Frame - Every two years spray the tubes with Waxol to stop internal rust.
Front Hub - If you are using a cartridge hub (I do) don't touch it until it fails. If you are using a cup and cone the I would be switching the bearing every year
Pedals - If I had an expensive pair of pedals then I might consider servicing then as it is life is too short, any half decent pedal should last 2 years+
Saddle - every few months I treat my leather saddle to some food. Even more occasional I give the tension screw a little tweak.
I am sure I have missed out an item or two!
All the above jobs can easily be achieved at home - given the correct tools. I am sure that bike shops are very good at doing all these jobs but I like to use my money elsewhere!
Stuart