There are several factors in designing floor systems
Normal Loading consists of Live Loads (people, furniture, etc.) and Dead Loads (carpet, subfloor, insulation, ceiling finish below, etc.)
The Code requires a minimum of 40 psf Live Load and 10 psf Dead Load. Check to see if your construction exceeds this minimum. You can google how much plywood weighs per square foot, insulation per square foot, carpet per square foot, ceramic tile per square foot, etc. (Ceramic tile weighs 3 times what carpet weighs.) Also, consider the live load: do you have a big family, treadmill, etc. that will be in this area.
Acceptable Deflection - Little known fact: the code does not specify a required deflection. It only says to account for deflection.) So, when you look up the maximum span for your I-joists, check to see how much deflection.
Lumber can deflect up to L/180 without failing, but it will feel spongy. Normal design standards is L/360 ...and some ceramic tile floors require L/720. (For L/360: 19’ x 12” per foot / 360 = 0.63” or about 2/3 of an inch.) Consider what type of floor coverings you’ll have in this area: carpet or ceramic tile?
Traffic patterns will reveal a spongy floor. You’ll notice a spongy floor when walking down a hallway or across a room before you’ll notice much deflection in a child’s bedroom, etc.
Also, what rooms are over the middle 1/3 of the 19’ span is important. Greatest deflection occurs in the middle third of spans.
By the way, we always add an extra joist or two under refrigerators, tubs, hot water tanks, waterbeds, etc. AND we decrease the spacing in Kitchens, Entry’s, Family Rooms, etc. (where people gather.)