It is not like you are building cables and deciding what lengths to purchase. You already own a pair of 19-feet long cables so just leave both sides at the same length. Cutting them will ruin the resale potential. If possible, run the short side around somewhere inconspicuous without coiling it up. You can always try coiling or not and determine whether you hear a difference.
You could always purchase and terminate bulk cable in the lengths you need. Try the linked cable. For your 10M needs, you will need two rolls of 25 feet, which would give you about 15M total. The cable is 10 gauge,
99.997% OFHC C10100 Copper
in foamed polyethylene insulation (FPE) - all for $21 per 25 feet! Check out the
pure copper (plated or unplated)
connectors (also from from the same vendor). You could be all-in at the lengths you need for less than $100. https://www.avoutlet.com/cables-connectors/bulk-cables/speaker/in-wall-cl3/furez-fz102as-25/