Yes, 5.5 bands is a decent score on the IELTS Listening test. Although a good score depends on the requirements of the institute you plan to apply to, a sub score of 5.5 bands in the IELTS Listening test is accepted by a majority of foreign universities. Learning the most common words in the IELTS Listening test will help you in scoring 6.5 bands or higher in the IELTS Listening test.