Should I split my data network into 2 separate VLANs?

Having desktop clients on a /19 gives you an incredibly large broadcast domain. That means DHCP requests, arp queries, mDNS, netbios, IPP printer discovery, etc. packets from a single host is getting replicated 550x. Generally, a /24 is the largest subnet that you'd want to put actual hosts in. Since you're in RFC1918 space, you can use a different /24 (or whatever) for every logical division you can come up.

The real question you should be asking is if you should be using smaller subnets. The answer to which is, "probably". If you choose to implement that with VLANs or not is really orthogonal.

Because your network is underutilized and you have only a few hosts, the only reason to split the /19 into smaller prefixes would be security. This means that you will use VLANs and a router to allow/filter the communication between VLANs.

Evaluate how much time will take to change the IPs and the applications that are using those IPs and see if it does worth to switch to other prefixes. With less resources you can find and eliminate unneeded broadcast generators, if they are affecting your network traffic.

If you add more hosts you can reach some limitations like the max number of MACs in the MAC address table of the switches, or the number of ARP entries in the ARP table on the router. If you reach this limit you will notice either high delays or strange behaviors (hosts that can not talk to each other, excessive broadcasts).

If you split your network in smaller prefixes, but you do not use VLANs, you will not reduce the broadcast traffic and you will not make your network more secure. Even if you split your network in VLANs, but you transport the VLANs on all switches (e.g. you are not using VLAN pruning) the broadcast traffic will affect all switches.

Some equipments, like Cisco switches, can limit the broadcast too (by rate or by type).

Network planning: Before doing any change create use cases with problems that you might encounter on your network and plan based on those assumptions.

550 hosts is not totally out of the question for a single subnet. You basically need to evaluate your own requirements. If broadcast packets are impacting (or are forecasted to impact) performance of your network in a way that impedes the function of your business, then you need to separate your hosts out into different subnets on different VLANs. If it's not impacting the business, then there is no need to do it.

It sounds like bandwidth isn't a concern, so there may be no business justifiable reason to invest in your infrastructure this way. Other reasons would typically revolve around security separations but only you would be able to tell us if your business has security needs that aren't being met with the current infrastructure.