Success! Adding 2 x 8GB RAM to my TS-451+. TrueNAS is running way better with the additional RAM. 8GB was enough just for basic file sharing but it did run into issues
Baie de stockage NAS QNAP TS-451+ - Baie de stockage - QNAP Algérie - CNIE
Memory RAM Upgrade for QNAP NAS TS-451 4GB DDR3 SODIMM | eBay
4GB Memory Upgrade for QNAP TS-451 DDR3L 1600MHz PC3L-12800 SODIMM RAM (PARTS-QUICK Brand) at Amazon.com
Memory RAM Upgrade for QNAP NAS TS-451 4GB DDR3 SODIMM | eBay