I worked over 30 years in aircraft, missile, and spacecraft wiring and electronic assembly, so you can take my comments for what you think they are worth...probably two cents.
If you are not experienced in making wire connections, you might be causing more problems than you are preventing when you solder crimp connections.
First, unless you are positive you are using non-activated solder and/or flux, you will be inviting corrosion wherever flux remains. All activated flux residue must be thoroughly cleaned with the proper solvent after soldering.
Second, if you use too much heat and the solder "wicks" inside the insulation beyond the insulation grip barrel of the termination, you have created the perfect condition for the wire to stress and break.
Third, if you install shrink sleeving over good solder, it can help with stress relief, but if you install it over bad solder, you are only hastening corrosion.
Solder over crimp, if done correctly, is like wearing suspenders with a belt...it's good insurance. However, if you don't know what you are doing, it's a recipe for bigger problems down the road.
FWIW, I almost never solder my crimped joints. High quality terminations on high quality wire, crimped properly, will function for decades without problems.
