I am sorry there is really no good workaround here. We had to do this multiple times for our past projects, sometimes we were fortunate to have of labelers work for us to get the manually annotated dataset build, rest of the times we did it ourselves.
Also, I am not sure you really require 15k data items, I would suggest
to start from as low as 1-2k and test the performance, based on the
particular case you might be surprised by the results.
Now to build your dataset, initially we used plain old excel sheets, and quickly it turned into a nightmare, excel is not designed for such tasks and looking at 1000s of lines of text and hand annotating in excel is super painful.
Here are some of the tools I would recommend:
Dataturks: https://dataturks.com: Very easy to use online tool, provides intuitive UI and you can have a team working on the dataset simultaneously. The output is fully compatible with openNLP, coreNLP etc.
GATE: http://gate.ac.uk/: Good old tool. Downloaded to your local machine, works well, a little pain to setup.
BRAT: http://brat.nlplab.org/: An open source tool, downloadable, does good job of tagging.
Hope this helps, happy tagging :)