Is an LVTTL output fully compatible to a TTL output?
TTL outputs must be able to sink 16 mA with a voltage drop of no more than 0.4 V, and to source 0.4 mA while staying above 2.4 V.
(TTL inputs source 1.6 mA, so this is designed for a fanout of 10.)

LVTTL outputs, as specified in JEDEC standard No. 8C.01, must be able to sink or source 2 mA at the same voltages.

So your LVTTL output will not be able to drive more than one TTL input, unless your component is specified for a higher current.