DURHAM — The investment capital keeps coming for Keen Decision Systems, a Durham-based marking software company, which already is growing rapidly. The startup has raised another $2 million and now has completed a planned $6.5 million fund raiser, according to an SEC filing. Six investors are backing the company. Keen was launched in 2010 and has generated interest with clients such as Campbell Soup Co., Church & Dwight Co., Eli Lilly and Co. and other Fortune 500 companies. It recently climbed 913 places to rank number 2,308 on the 2020 Inc. 5000 list. Privately held firms are ranked based on three years of revenue. Keen noted its 3-year growth was nearly 182%.