I would strongly recommend you to wire your terminal with ethernet cable and a Gigabit switch or router. Its also worth mentioning that cutting down on any unnecessary traffic on POS network can really make a difference in delays. I always keep guest network separated on a different router.
Upgrade to 4GB of RAM. There is a big difference when your database is 5MB and over 100MB. That difference can be seen on older outdated hardware.
Windows updates are a big factor but using multiple Windows user accounts. Being logged in on for example Admin and Guest account on windows can cause massive delays even on newer machines. Its really important to make backups before Windows updates. Sometimes they can fail after a power cut or some unusual error.
SSDs can make a big difference when installed on the server. It has huge difference in read/write speed compared to normal hard drives. Make sure you make hourly backups with triggers if you have an SSD. They need to be synced with a cloud because cheap commercial SSDs tend to have a short lifespan.
Never use WiFi unless you have Android or Windows tablets/phones. And if so, use high gain antennas for good coverage and reliable use. I use 12 dBi antennas for coverages on the beachfronts or big restaurant terraces and never had an issue with that kind of setup.