Well, that's a little on the low side, but I think it'll work. Give it a try anyway. I've found with tenellus that it can take some time to settle in.
The stuff that's running rampant in my tank at the moment sat around and did nothing for about 6 months. Mind you 4 of those months were unbelievably hot and most of my plants died or just hung in. After the temperatures cooled and I was cleaning and rearranging I found 2 of the original 4 little, tiny tenellus plants. I was amazed that they were still alive. Anyway, I moved them to their own corner and bam, now they're 6" tall and ready to take over.