I am planning to invest in Ethernet over Fibre-to-the-Cabinet (EoFTTC) connection - this is something close to a full fibre leased line, except that the "last mile" runs on bonded copper cables. It provides pretty much the same reliability, guaranteed by SLA, as the fibre leased line. However, the speed is limited to a guaranteed 15 Mbps and latency to 10 ms. Will that speed be sufficient for scalping/very short-term day trading?
How many trades per day do you do, and what's their typical duration? I ask because the speeds you're talking about would be perfectly adequate for any kind of fast-moving, very short-term intraday trading I'd ever want or need to do, but I know that they'd be absolutely hopeless for scalping. I strongly suspect, though, that in using the expression "scalping/very short-term day trading", conflating the two, you're actually using the word "scalping" with a very significantly different meaning from its general accepted one in the industry ... and if I'm right with that suspicion, then you almost certainly have nothing to worry about at all.
15Mbps refers to how much you can download at once, not really the speed. Yes, when downloading a 1 gigabyte movie, you want more bandwith since it will ultimately finish sooner, but when it comes to trading, its different. Even if you monitor 100 instruments at the same time, I doubt this mean you're having to download 1.8 megabytes per second, which is what 15Mbps refers to. For my trading, with TWS open and watching 4 futures instruments in real time plus other symbols that are updating in real time, I see that my usage is about 10-20kbps (kilo bytes per second). Now if I also browse the intent, this jumps to maybe 100-500kbps, but still well below the 1.8 megabytes per second that your 15Mbps connection would theoretically top out at. So your connection will have no problem what so ever for trading. The latency of course is another factor. I'm not sure what the 10ms refers to. This is usually a number of how quickly a signal gets from your house to somewhere else. You might want to ping the server of your broker, to see how quickly a signal gets there. The broker of course has to also send this to the exchange. I'm not an expert in this field, but if you consider that your brain might need about 200ms or more to even interpret something you see, and then even more time to click a button, this will be the rate limiting stop. If you're in the US, the duration of the transmission really won't be a factor. But honestly, you can't win the speed game at home. If trading limit orders, you'll always be at the back of the que, and if trading market orders, its possible that the bid/ask has moved from when you click to what it is when its filled. This isn't because of a slow connection, but because your brain is like a turtle trying to compete with a cheetah.
It isn't the bandwidth that is important; it is latency. Your data price data isn't like streaming a video from porn hub, there isn't all that much bandwidth used. The thing you need to watch is the latency to your broker.
Cable in my area is not so good so I use T-1, I rent servers through couple companies I pay by month for automation trading. https://www.speedytradingservers.com/ I think the speed for uploading more important than download speed. Number of pings to your software company if you have that then to your broker etc...
I'm also using speedy since every time Ninja trader disconnects it doesn't reconnect reliably. (at least it didn't for me). Instead of a T1 I am using multiple Cell providers 4G data services through a cradlepoint router with failover capability.
I know it isn't from the internet being slow; it is from the connection being dropped. When I have had drops in the past I would have to "reconnect" to my data feed in Ninja and worse yet you had a few seconds lag before figuring out you had no data. Now that I am using speedy trading servers Ninja never disconnects from my feed. I admit Ninja Trader doesn't handle disconnects well. It should automatically try to reconnect if the connection is lost.