How fast orders are filled on a real environment

Hello, which ecn is used for placing orders in the real environment? My question is how fast a limit order will be in the market , to get filled (e.g. if a stock is moving extremely fast). For now, I’ve been testing on a paper account.

I’m trading stocks, that are moving extremely fast (need to have second-defined level entry/exit).

this is a common slippage problem, and total disappointment for me.

when I open a position, I put bracket orders with TP&SL rates.
when the market hits either SL or TP, I see my position is closed far from the bracket most of the time (~90%), especially on the SL side.

interestingly, I have rarely seen slippage on the TP side, that is at a more than preset/expected profit.

this problem holds especially for those stocks with low rate (<$5), and with low volume.
until SL&TP are converted to market orders and until executed, the market moves far outside of the pre-set bracket limits.

I have tried this on both paper and live accounts, it is pretty much the same.

It could be normal to have slippage on a stop loss on stocks with low volume, e.g. if for example the bid is lower than your limit order. The question is that if for example there is a bid of 200 shares at 4.5$ and you sell at 4.5$, is it going to happen instantly, or it will take seconds? (It depends on which ECN they use as well for routing the orders, hopefully direct routing is using).