why go so dramatic in change, from traditional to compact, when this is a temporary start-up situation?! you have not been riding in awhile and that means your body is not at its peak and needs time to build base miles, endurance, strength, flexibility, etc. -- give it time!

as for gearing, why not take the less expensive route and chain your rear cassette to something with lower gearing, keeping your higher gearing cassette on your trainer bike ... you can eventually change cassettes depending on your development/training. Shimano makes a 12-27, which may give you the lower gearing you need right now ... just thoughts.