We have a last 10 years of article approximate 1500. Now we need to upload all this articles in OJS. We already try but file is not uploaded successfully. Our website is www.njcmindia.org. We have a rss feed look like DOAJ.
For such a large collection of articles, the XML import feature might be a good way to go, however, there would be considerable work involved in creating the files necessary to import 1500 articles into OJS.
Native XML Import is the way to go, as @rcgillis pointed out. We recently imported more than 5600 articles and 303 issues this way from a non-OJS system.
If your system can export the metadata (and even the PDFs as base64-encoded), one can transform the source XML to the OJS XML import format using XSLT. My recommendation is to find a developer who is experienced in PHP and XML/XSLT.