Why the position barely moves
The tropical year runs about a quarter of a day longer than the calendar year, so the Sun arrives at each seasonal marker roughly six hours later with every year that passes. A leap day then pulls the calendar back by a full day and the drift starts over. Four steps forward, one step back, indefinitely.
The effect on a fixed calendar date is a small oscillation rather than a slide. Taking noon in every year from 1930 to 2035, the Sun on 15 July has stayed inside a band about a degree and a half wide, from around twenty two to around twenty three and a half degrees of Cancer. Your birth year decides where in that band you fall, and no year takes you outside it. Anyone quoting a single fixed degree for the date has rounded, and anyone refusing to quote one at all has understated what can be known.
What sits at that degree
Twenty two degrees places the Sun in the closing ten degree stretch of Cancer, the third of the sign's three faces. In the Chaldean order that band belongs to the Moon, which also rules Cancer itself, so the sign ruler and the face ruler are the same body here. The triplicity scheme reads the same degrees through Pisces and hands them to Jupiter.
Traditionally the doubled lunar attribution is read as a strengthening of what the sign already describes, an emphasis on memory, attachment and indirect approach, rather than as a separate flavour laid on top. That is interpretation and worth marking as such. The position is the checkable part. It can be confirmed against any ephemeris, which is not true of a single line of the reading built on top of it.
How far the boundary is
The Sun leaves Cancer at thirty degrees, so a 15 July birth has around seven degrees of the sign left, which is about a week. That is a comfortable margin. No birth hour and no time zone brings the Leo crossing within reach, which is why this date is settled in a way that dates in the low twenties of July are not.
It is worth stating the difference clearly, because the two situations get written up identically. A boundary date is genuinely uncertain until you supply a year and an hour. This one is certain from the calendar alone, and the year and hour add precision instead of resolving doubt.
What the degree is actually for
A degree is not a personality reading. It is a coordinate, and its uses are technical. Aspects between planets are measured in degrees with a tolerance of a few either side, so knowing the Sun sits near twenty two rather than somewhere loosely in Cancer decides whether another planet is in aspect to it or not. Solar returns and progressions work off the same figure.
The widget above takes your year, your hour and your birthplace and returns that exact degree rather than the noon approximation used here, along with your distance from the nearest sign boundary. For this date the distance will be large, which is a useful thing to have confirmed rather than assumed.
Questions people ask about this
Is 15 July always Cancer?
Yes. Every year sampled from 1930 to 2035 puts the Sun in Cancer on this date, roughly a week short of Leo. The birth hour and the time zone make no difference to that.
What degree is the Sun on 15 July?
Between about twenty two and twenty three and a half degrees of Cancer, depending on the year. The widget above returns the exact figure once it has your year, hour and birthplace.
Why does the degree change slightly year to year?
Because the calendar year and the orbital year are not the same length. The Sun arrives about six hours later each year until a leap day resets it, which produces a small repeating cycle rather than a drift.
Which decan is this?
The third decan of Cancer, from twenty to thirty degrees. The Chaldean order gives it the Moon and the triplicity scheme gives it Jupiter through Pisces.
Does a high degree mean a stronger sign?
No. A Sun at twenty two degrees of Cancer is exactly as much in Cancer as one at two. The degree matters for aspects, houses and timing techniques, not for how much the sign counts.
What does the date leave open?
Everything that moves faster than the Sun or depends on the horizon. The Moon can be in either of two signs across a single day, and the rising sign can be any of the twelve.