Help with drawtext

I'm trying to create an indicator that records lvl2 depth ( volume and price) to a dataseries and then draw text of that dataseries at the bar it was associated with. Im able to collect and then draw the text, 10 ask levels and 10 bid levels per bar using a range bar chart.

I'm writing to the dataseries OnMarketDepth() to get the current depth and then using drawtext OnBarUpdate() for each level of depth to draw past bars bid/ask depth to 10 levels. after a few hundred bars my cpu usage starts increasing and scrolling the chart becomes very slow.

Whats the most efficient way to do this? Drawtext I hear is cpu intensive.