People say about a general rule of thumb of spending no more than 10% of revenue into marketing.
Depends on your size, the % will be different, but your marketing expenses sound pretty low. Spending on marketing is a way to bring LF up, so why do you care if you have great LF?
In MT7, I'm spending 5%, my CI is 49 and rising
In DOTM4, I'm spending 7%, my CI is 61 and rising
Hope that helps