Low relative to what it should sell? Maybe, but that's hard to judge. Low relative to what my target sales are? No, because I had no target really, since it's the first game I'm selling anything more than 0 is high. I originally predicted 100 sales in a year; it's been less than 6 months and there's been 150 sales, so it's high relative to my original expectations when I decided to sell it.
Could it be higher? Probably. There are likely many small things I could do that would double or triple the sales, I just haven't found them experimentally yet. For example, it could be that the better trailer would lead to a higher percent of the people who visit the site downloading it; it could be that using banner advertising would double the sales, or perhaps what would do that would be simply putting in a "nag window" when a player exits the game, asking them to remember to support us; I can't really know until I try those things.
Perhaps sales are already at their near-maximum, with the number of people who like abstract plot-driven tower defense games being low enough that this is about as high as it gets. Perhaps the level editor will help. It's all speculation really, I suspect most marketing people pretend to know more than they do, the marketplace is way too complex for a human to understand. It's best to just create the best things you can and accept what results appear (a tenet of Karma Yoga).
I am still planning on doing the marketing strategies though; getting it on a portal like Manifesto is one of those. Marketing work too is creative work. I also did Google Ads back in September (which didn't amount to anything useful at all, something like 100$+ spent for 300 clicks, which is next to worthless), which was a success because I learned that it didn't work, at least in the ways that I used it (I heard it's useful if you use it to gather a large newsletter and then sell to that newsletter, but I don't plan to use that method to sell games in the foreseeable future). I'm going to continue with the other marketing methods too but am behind schedule; I think a new one a month is more sustainable than a new one a week as I originally planned (easier to measure the results of too).