No you don't need to upgrade your lighting but as is the stem plants may not flourish. Using a liquid carbon daily will aid plants in photosynthesis and growth especially in lower light tanks. It helps them to utilize the light that they do get. I run 2 low and I mean low light tanks, use liquid carbon daily, and grow a variety of plants, including some stem plants that normally couldn't be grown in that light level. I'm not saying liquid carbon is a miracle additive but it definitely helps a lot. Plus even low light plants do much better with ferts and I don't consider those stem plants, which I can't identify as I'm pretty sure they aren't in their submerged form, low light.
You can buy Metricide 14 Day Solution on line for about $20 and $7 for shipping, mix it at a 1:1 ratio with RO or Distilled water, and get 2 gallons for $27 bucks. That is dirt cheap compared to a name brand like Excel. Start dosing at 1ml per 10 gallons of tank water and after a couple weeks increase dosage to 1ml per 5 gallons of tank water.
If you start using Glut and give the plants ferts you will see improvement. You can always upgrade lighting down the road if you want.