Writing a fanfic? Want some accuracy? Here is a (mostly) headache free and reliable timeline of the MCU as well as chapters discussing specific movies and timeline controversies. Spoilers guaranteed.
Best to read introduction before leaving comments...
I can't prove this movie took place in 2015. All I can do is point to evidence showing it had to happen a year from CA:TWS.
Opening scene, Avengers have located and invaded Strucker's base. It's snowy in Sokovia which is somewhere in Eastern Europe. Thor's relief at finding the scepter "at long last" shows it's been a while since SHIELD fell. The twins, who we last saw practicing their newfound abilities after the fall of SHIELD, are considered by Strucker to be unprepared to fight the Avengers.
Sidepoint, after Steve first encounters Pietro, he says to Thor, "All the new players we've faced, I've never seen this." Meaning, naturally, that there are other "enhanced" characters that Hydra has been throwing at the Avengers since CA:TWS.
Back to timeline; we see the Iron Legion who debuted in IM3, and are formally introduced to the remodeled Avenger Tower which appeared briefly in CA:TWS. Thor allows Tony to study the scepter until he leaves for Asgard after the planned victory party, {"Just a few days till the farewell party."}
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which is on a Saturday {Tony: "And, Helen, I expect to see you at the party on Saturday."}
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so Tony begins studying the scepter on a Wednesday {Tony: "That's three days. Give me three days."}
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