I have Geoserver 2.11.2,PostgreSQL 9.5,open layers 3 and Tomcat 8 all are installed on Ubuntu 16.4 Azure cloud virtual machine.I also enabled GeoWebCache but still WMS layer rendering speed is slow(15 to 16 seconds).Please find this .Is there any idea to improve more speed than the current speed of web-tool,Thanks.
Broadly, it sounds like something is misconfigured. There are some excellent resources in the GeoServer docs (http://docs.geoserver.org/stable/en/user/production/) about running in production. From GeoSolutions, there is some training materials (http://geoserver.geo-solutions.it/edu/en/enterprise/index.html) and talks (https://www.slideshare.net/geosolutions/geoserver-in-production-we-do-it-here-is-how-foss4g-2016) which address common techniques for data prep, JVM options, and other considerations which may help some.
As a particular call-out, I'd strongly suggest Marlin (https://github.com/bourgesl/marlin-renderer/wiki/How-to-use). Its use in GeoServer can help immensely with concurrent rendering (http://www.geo-solutions.it/blog/developerss-corner-achieving-extreme-geoserver-scalability-with-the-new-marlin-vector-rasterizer/).
It may be worth making sure that PostGIS is installed and that your data has a spatial index. Tuning PostGIS is a separate topic.
Once the data is prepped and indexed and Marlin is up and running, it may be worth seeding the GWC cache. With that, your application would just be serving pre-baked tiles for coarse zoom levels and that should be snappier.