A fifteen-minute delay can support learning and slower research. It cannot support second-by-second claims or certify an executable price.
Delay and bar interval are different
A 15-minute bar may aggregate trading into a 15-minute interval. A quote delayed by 15 minutes reports an older market state. A feed can have one, both or neither characteristic. Always display the observation timestamp, receipt timestamp, timezone and source entitlement separately.
The “last trade” time is not a substitute for the bid/ask observation time. An option may trade infrequently while its quote changes.
Reasonable beta uses
Delayed data can help exercise workflows, compare strategy structures, test deterministic calculations and conduct research where immediate execution is not implied. A user can refresh prices on a broker before deciding whether to place an order.
It is unsuitable for promises of live scanning, immediate alert fills, 0DTE microstructure timing or second-level accuracy. Fast events can make a fifteen-minute-old chain economically unrelated to the current market.
Upgrade gates
Before moving to real-time data, verify contract coverage, every-leg timestamps, Greeks/IV methodology, corporate-action handling, rate limits, historical rights, personal versus commercial licensing and redistribution restrictions. Faster transport cannot repair missing or ambiguous fields.
Run the same saved test cases against delayed and real-time feeds before trusting the upgrade. Differences should be explainable by timestamps and documented methodology, not silently absorbed into a new signal score.