In my opinion a "low" oil temp like 150F is not a particular worry.  I would wonder if the vernatherm is working correctly - your OAT's were not particularly low - what would happen if they were -20, not unheard of at high altitudes in the winter?  Anyway, operating with  the temperature lower than "normal" will increase engine friction due to the higher viscosity of the oil, but with the semi-synthetic that effect is not as large as if you were running a single-weight mineral oil.  Yes, the lower oil temperature reduces the evaporation of water from the oil, but even 150 isn't too bad although 180 would be better and 200 or more would be best.  Yes, changing oil a little more often in the winter might be a good thing, but you mentioned a 25-hour oil change interval, which I would consider to be "drastically" short, especially with a synthetic blen.  With a good engine oil change intervals of at least 50 hours and even 100 hours would make sense.  A good way to judge the correct interval is to look at the oil - if it looks "ugly" it might be time to change it.  Too much water will turn it a milky, brown color and in that case you can either change the oil or run the engine for a while with the oil hot to cook out the water.  An opaque gray color means it is contaminated with lead oxide - been running really rich?  If the oil turns black it might be time to change oil, at least after a while.  My rule of thumb is that I keep the oil in there twice as long as it takes to turn black (how black?  I don't know) or until 50 hours or so.  With my new engine the oil is still relatively clear at 40 hours, so I should wait until at least 80 hours to change it (EXXON Elite), but I'll probably get impatient at about 50.  In my old Cessna TR182 the book said to change the filter at 50 and the oil at 100, but I figured if I went to the trouble to change the filter I might as well change the oil.  The plane was used regularly, so corrosion wasn't much of an issue and I would use the 50-hour mark as a time to start to think about changing it - the actual intervals varied between 50 and 80.  Bottom line:  I don't subscribe to the idea that changing oil really often is "cheap insurance" - insurance is only cheap if it actually insures against something and if the oil hasn't been in there for more than 6 months or so and still looks good there is really nothing to be gained by changing it.  I feel that any servicing is often a bigger risk - are all the bolts tight, was there anything left off, etc.